The photolithographic process for the GPC (Giant magnetoresistance Permanent magnet Conductor) layer requires high resolution (smallest dimension) and the tightest control for CD (critical dimension) uniformity. With smaller and smaller design rules being introduced for the track width, a large process window or depth of focus is needed. Several resolution enhancement techniques can be used to widen the process window but each of these has its own limitations or is unsuitable for thin film head applications. For example, the cost of modifying masks by adding sub-resolution features generated by OPC (optical-proximity-correction) software is substantial.
As another example, off-axis illumination has been proven to improve both resolution as well as depth of focus but works well only in areas where the local pattern density (fraction of the area that is opaque) can be considered to be at least semi-dense (generally about 20% opaque).
The thin film head industry faces a unique situation in that there is often a need to form an etch mask containing a single isolated line in order to be able to etch through the topmost layers of a read head (typically a Giant Magneto Resistance, or GMR, stack). The present invention discloses how such a mask may be formed without the need to use expensive OPC techniques to assist in the formation of said mask, including said single isolated line.
A routine search of the prior art was performed with the following references of interest being found:
Mansfield et al. describe assist features for photolithographs in U.S. Pat. No. 6,421,820. In U.S. Pat. No. 6,303,252, Lin discloses assist features between! semi-dense lines. U.S. Pat. No. 6,165,693 (Lin et al) shows a method of designing assist features. None of these patents are in the magnetic recording field. U.S. Pat. No. 5,491,600 (Chen et al) is an example of a patent in the magnetic recording field showing a PMGI layer for lift-off of a photoresist.